1. Field of the Invention
The present invention relates to a method, system, and program for managing path groups to an I/O device.
2. Description of the Related Art
In certain computing environments, multiple host systems may communicate with multiple control units providing access to storage devices, such as interconnected hard disk drives, through one or more logical paths. The interconnected drives may be configured as a Direct Access Storage Device (DASD), Redundant Array of Independent Disks (RAID), Just a Bunch of Disks (JBOD), etc. For instance, the hosts may implement International Business Machines Corporation's (IBM®) Transaction Facility Processing (TPF) operating system in different processing systems in the hosts that issue Multi-Path Lock Facility (MPLF) locking requests to a control unit, such as an IBM Enterprise Storage Server (ESS)®, for data in a storage device managed by the ESS receiving the request. (IBM and ESS are registered trademarks of IBM). The ESS server microcode manages the locks for resources requested by the hosts using the TPF software.
A host granted a lock to a storage resource by the ESS lock manager may have exclusive or non-exclusive access to a track or data in the storage devices managed by the ESS. In this way, the ESS server manages locking for requests from many host systems.
In host systems implementing the IBM Enterprise Systems Architecture/390® (ESA/390), the processing systems executing in each host may comprise logical partitions of a processor, which divides a single processor into two or more logical independent processing systems. (IBM Enterprise Systems Architecture/390 is a registered trademark of IBM) Each logical partition communicates with one or more ESS servers, or other control units, over one or more logical paths.
Each TPF host connected to a logical partition in the ESS is a unique user of that partition. When a user connects to a logical partition, the path and device on which the host connects are retained as the connection path and connection device. This connection path and device may be associated with a particular path group comprising multiple logical paths to a control unit. However, the host TPF software may issue the disband path groups command for the intended connection path and device prior to connection. A user may connect on any logical path into the ESS.
In the current art, a user within a logical partition executing TPF software or other software capable of issuing the MPLF specific command set, may communicate a lock request to a control unit down a logical path. This path may or may not be the connection path and may or may not be in a path group. If the user cannot get the lock and the user has requested to be queued as a waiter, then once the lock becomes available for the user to hold, the ESS sends the user an attention interrupt and message to notify the user that the user is a holder of the lock. Until the user receives such attention, the user cannot process the user's I/O and the user's single threaded queues will increase while waiting to obtain the attention and the lock. The attention is required to go to the connection path/device. If this connection path/device is within a path group, then as per path group architecture, the attention may go to any path in the path group for the device. However, with the path group architecture, the attention may be sent on a path in the path group to a host/user other than the user host/user to which the attention is actually intended. In such case where the attention is sent to the wrong user, the user is unaware of holding the lock due to not receiving the attention and notification. As a result, the user will not process queued requests and the queue will increase. In addition, if the processing system requesting the lock does not get the attention, then the further waiters of the lock will not get processed because the current new holder did not respond to the attention message from the ESS locking facility.